Carbon-Reinforced Nb2CTx MXene/MoS2 Nanosheets as a Superior Rate and High-Capacity Anode for Sodium-Ion Batteries.

Sodium-ion batteries operating at room temperature have emerged as a generation of energy storage devices to replace lithium-ion batteries; however, they are limited by a lack of anode materials with both an adequate lifespan and excellent rate capability. To address this issue, we developed Nb2CTx MXene-framework MoS2 nanosheets coated with carbon (Nb2CTx@MoS2@C) and constructed a robust three-dimensional cross-linked structure. In such a design, highly conductive Nb2CTx MXene nanosheets prevent the restacking of MoS2 sheets and provide efficient channels for charge transfer and diffusion. Additionally, the hierarchical carbon coating has a certain level of volume elasticity and excellent electrical conductivity to guarantee the intercalation of sodium ions, facilitating both fast kinetics and long-term stability. As a result, the Nb2CTx@MoS2@C anode delivers an ultrahigh reversible capacity of 530 mA h g-1 at 0.1 A g-1 after 200 cycles and very long cycling stability with a capacity of 403 mA h g-1 and only 0.01% degradation per cycle for 2000 cycles at 1.0 A g-1. Moreover, this anode has an outstanding capacity retention rate of approximately 88.4% from 0.1 to 1 A g-1 in regard to rate performance. Most importantly, the Nb2CTx@MoS2@C anode can realize a quick charge and discharge at current densities of 20 or even 40 A g-1 with capacities of 340 and 260 mAh g-1, respectively, which will increase the number of practical applications for sodium-ion batteries.